This invention relates to wireless communications systems and, more particularly, to wireless communications between wireless terminals and base stations.
In wireless communications systems, wireless terminals can maintain connectivity to a base station without actively communicating with the base station. Such wireless terminals are referred to as being in a paging mode. In such a system, the wireless terminals (WTs) are paged by associated base stations (BSs) to initiate communications. In order to realize this, the base stations typically have a channel on the downlink called the paging channel. In prior known paging arrangements, the paging channel is subdivided into a plurality of paging time slots. A group of wireless terminals is typically allocated a paging time slot of a prescribed periodicity for receiving paging messages from associated base stations. As shown in FIG. 1, wireless terminals #1 and #2 are allocated to time slot A, wireless terminals #3 and #4 are allocated to time slot C, and so on. Each mobile unit is expected to monitor for paging messages from an associated base station during these paging time slots. Thus, in the example shown in FIG. 1, wireless terminal #1 and #2 only monitor time slots A and B, while wireless terminals #3 and #4 only monitor time slots C and D, and so on. To this end, the periodicity of the paging time slots is made sufficiently long that the each of the wireless terminals can effectively turn off most of its circuitry between two of its designated paging time slots and, thus, save energy. This is referred to as the wireless terminal entering a so-called xe2x80x9csleepxe2x80x9d mode. The wireless terminal, even though in the sleep mode, still has to keep track of the received paging time slots. The wireless terminal is caused to xe2x80x9cwake upxe2x80x9d prior to the arrival of its designated paging time slot, tunes to the downlink channel and achieves carrier, timing and frame synchronization. Then, the wireless terminal decodes the paging time slot and if its identifier is included in the wireless terminal""s designated paging time slot, it knows that the page message is meant for it. The wireless terminal then takes the appropriate action indicated in the paging message. If the paging message is not meant for the wireless terminal, the wireless terminal returns to the xe2x80x9csleepxe2x80x9d mode, and monitors the next received paging time slot designated to it.
As seen in FIG. 1, more than one wireless terminal shares the same paging time slot. The rationale for this is that in general paging messages for a particular wireless terminal do not arrive very often, and paging messages for different wireless terminals arrive at mutually independent time slots. Consequently, sharing of the so-called paging time slots among several wireless terminals is a more efficient way of utilizing the paging channel. A problem of sharing of the paging time slots among several wireless terminals, however, is that latency in receiving a paging message is increased when several paging messages arrive simultaneously for the wireless terminals sharing a particular paging time slot. For example, consider that paging messages arrive in time slot A of FIG. 1 for both wireless terminals #1 and #2, then the associated base station can only transmit one of the paging messages in time slot A, for example, the message for wireless terminal #1. Then, the base station must wait until time slot B to transmit the paging message for wireless terminal #2. Depending on the arrival rates of paging messages and the number of wireless terminals sharing a paging time slot, the latency may become undesirably long.
Problems and limitations of prior wireless communications systems paging arrangements are overcome, in one embodiment of the invention, by employing a unique paging xe2x80x9csuperxe2x80x9d time slot format. A paging super time slot includes a plurality of prescribed time slots. Each wireless terminal is associated with cyclically recurring super time slots. A super slot is associated with one or more wireless terminals.
A base station always selects the first available time slot in a super time slot to transmit a paging message to a wireless terminal that is associated with the super time slot. Each wireless terminal monitors every time slot in the associated super time slot until either detecting reception of its associated paging message or detecting an empty time slot.
In another embodiment of the invention, a unique partially overlapping super time slot format is employed in which a super time slot has at least one time slot common to its adjacent super time slots. This allows wireless terminals associated with adjacent super time slots to share the common at least one time slot. In turn, this results in balanced traffic loads, smoothed traffic fluctuation and reduced congestion.
A technical advantage of the invention is that latency in a base station transmitting a paging message and, hence, in a wireless terminal receiving a paging message is significantly reduced.